To recover a hydrocarbon resource from a subterranean formation, wellbore casings or pipes are typically coupled together in end-to-end relation within the subterranean formation. Each wellbore casing may be rigid, for example, and be relatively strong. Each wellbore casing may include steel.
To more efficiently recover a hydrocarbon resource from the subterranean formation, it may be desirable to apply RF power to the subterranean formation within (or adjacent to) the hydrocarbon resource. To accomplish this, a rigid coaxial feed arrangement or transmission line may be desired to couple to a transducer in the subterranean formation. Typical commercial designs of a rigid coaxial feed arrangement are not generally designed for structural loading or subterranean use, as installation generally requires long runs of the transmission line along the lines of 500-1500 meters, for example. As an example, a typical overhead transmission line may be capable of 1,000 lbs tension, while it may be desirable for a downhole transmission line to have 150,000 to 500,000 lbs tensile capability, which may amount to 150 to 500 times the capacity of an existing commercial product.
One approach to a rigid coaxial feed arrangement uses two custom aluminum assemblies, one structural tube and one coaxial assembly therein. This approach may have a reduced cost, increased structural performance, increased ease of assembly, and increased compliance with oil field standards. Additionally, a high conductivity pipe (copper or aluminum) may be selected for a best galvanic match to a desired wellbore casing. A custom threaded aluminum coaxial transmission line may address this. However, aluminum is strength limited and generally will not handle structural load requirements without a secondary structural layer.
To address this, one approach uses a primary structural tube with a supported (floating) coaxial transmission line carried therein. The structural tube assumes the installation and operational loads.
U.S. Patent Application Publication No. 2007/0187089 to Bridges et al. discloses an RF technology heater for unconventional resources. More particularly, Bridges et al. discloses a heater assembly for heating shale oil. The heater assembly includes an inner conductor and an outer conductor or well casing electrically isolated from the inner conductor. Copper, or aluminum is coated on the interior of the outer conductor or casing to maintain temperature, increase conductivity, and maintain a robust structure.
Another approach is disclosed in U.S. Pat. No. 5,455,548 to Grandchamp et al. Grandchamp et al. discloses a structural RF coaxial that uses a bolt and flange method for assembly. A drawback to this approach is that assembly time may be significant.
It may thus be desirable to provide a relatively high strength coaxial transmission line for use in a subterranean formation. More particularly, it may be desirable to provide a high strength coaxial transmission using less components, and that can withstand relatively high stresses associated with hydrocarbon resource recovery in a subterranean formation.